Leptin is released from the fat cells - it's called an adipocyte. The more fat you carry around with you, the more leptin is formed. This hormone, which was only discovered in 1994, has the main task of transmitting a satiety signal, stopping food intake and increasing energy expenditure. A natural appetite suppressant that is often in the limelight of weight regulation due to its function.
In simple terms, the underlying mechanism is as follows:
If the fat stores in the body are well filled, they release leptin. This in turn gives the brain to understand that nothing more needs to be eaten, the feeling of satiety increases. The energy consumption is also increased - nothing needs to be stored anymore, the required energy can be used from the love handles. Leptin basically says: enough energy stored! Stop eating!
The principle behind it is shown schematically here:
If, on the other hand, you only have a small amount of fat, only a little leptin is formed and released. Leptin pills does not transmit a saturation signal - the body should be refueled with new energy (food). The energy consumption is reduced so that the body does not run the risk of running out of fuel.
You can imagine it schematically as follows:
It should be mentioned that these processes are not fast, short-term signals. So not: eat the muffin, leptin rises and that's why you're full. Other mechanisms are mainly responsible for this type of satiety. Leptin pills is more of a kind of fuel gauge in the fat stores that provides information about long-term reserves.
How important leptin is for the regulation of our metabolism is also clear from the following observation: People who cannot produce leptin do not feel satiated and become very overweight even in childhood. In these extremely rare cases, the administration of leptin leads to a drastic decrease and to normalization of weight.
Incidentally, there is also a hormone that does exactly the opposite: among other things, ghrelin is responsible for making us feel hungry. However, it is not released from the fat cells, but from the stomach and pancreas.
Back to Leptin: It's actually pretty clever what's going on. Leptin protects the body in a certain way from accumulating more bacon and thus keeps the fat stores in balance.
So what more do you want?
When the effects of leptin fail - leptin resistance
Once again, real life brings us back down to earth - everything doesn't go as easy as you would like it to be.
Since leptin has a filling effect and can thus counteract obesity, it has been examined in numerous studies for a potential use for weight loss. Put simply: inject leptin, be fuller in the long term, and lose weight. That's the theory. Unfortunately, the administration did not achieve the desired results in practice.
How can that be? Shouldn't leptin curb hunger?
You would think so, but leptin is not lacking in overweight people - on the contrary: it is present in large quantities! One speaks of a so-called hyperleptinemia. Despite these high amounts of leptin, a sufficient signal of saturation is not achieved. The mechanisms described above are the ideal state in full health and without being overweight or underweight. As soon as this situation drifts in another direction, the whole thing falls apart.
In the case of overweight, one usually comes across the term leptin resistance - a condition in which high amounts of leptin can neither trigger satiety nor weight loss.
The following graphic summarizes the state of leptin resistance schematically: If you are overweight, fat cells release a lot of leptin (state of hyperleptinemia). However, there is no effect, no saturation signal is generated and the energy consumption is not increased either. As a result, food intake continues to increase and the vicious cycle is in full swing.